Specialized radiographic techniques /certified fixed orthodontic courses by Indian dental academy

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IN DIAGNOSTIC AIDS

INDIAN DENTAL ACADEMY
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www.indiandentalacademy.com


Specialized radiographic techniques


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Digital subtraction radiography
Xeroradiography
Ultrasonography
Laser holography


Digital subtraction radiography


• Requires two different images and the
subtracted image is a composite of
these two images representing their
different densities


• Sensitive enough to detect a .12 mm
change in the cortical bone.
• The ability of this technique to detect
minute changes is dependant on the
degree of matching of the two images.


Technique
• In DSR two standardized radiographs of
anatomical region are made with
identical exposure geometry at different
time period.
• The first radiograph is considered a
reference image while the second
radiograph taken at a later date is the
image to be compared.

• The first reference image is digitized
and converted to a exact positive image
by the computer and displayed on the
TV screen as a positive image.
• Then the second image is
superimposed on the positive reference
image


• Any differences between the two
images will be shown on neutral gray
background as brighter or darker areas
depending on the nature of tissue
changes.


• By this process a radiograph is
converted to an array of points each of
which has a specific optical density.
• If each points of identical images is
subtracted the result will be a neutral
gray image.


• In clinical practice the two radiographs
are taken one after he other ,after some
time presuming some tissue changes
have occurred
• In DSR the changes otherwise not
clinically visible are seen with subtle
change in the densities of the two
radiographs.

Procedure
• Digitization
• To digitize a picture is taken using a
video camera
• Then computer digitizers place a grid
over the radiograph and convert the
continuous gray scale to different
numbers between 0 –255


Limitations
• Diagnostic information can only be
obtained when orientation of the x ray
source,object and the image receptor is
highly repeatable.
• Subtracted image must be of the
identical anatomical region.
• Density and contrast of the original
image should not effect that of the
resulting image.

Overcoming the limitations
• Computer algorithms have been
developed for overcoming the variation
in density and contrast.
• The occlusal stants can be used to
stabilize relationships between teeth
film and x ray source.
• Cephalostat can be used to stabilize x
ray films and the teeth.


• Computer can be used to correct
distortion caused by film placement
• Reference points can be used to
superimpose sequential radiographs.


Applications
• Useful in diagnosis of periodontal and
carious lesions. (both of which are
characterized by insidious and slow rate
of resorption).


Applications
• Used for quantitative estimation of mass
or volume of a lesion. measurement
can be measured with the help of a
wedge.


• Contrast enhancement with image in
color can detect small change in bone.


• Useful in detection of small changes in
mandibular condyle position and
integrity of articular surfaces and or
remodeling around granular
hydroxyapatite implants.


• Assessment of failure of implant therapy
and progress of periodontal therapy.


Image enhancement of mandibular
condyle through digital subtraction
• OOO 1987 ( south had et al )


Radiographic evaluation of the effect
of orthodontic retraction on the root of
the maxillary canine
• Perona and wenzel (dentomaxillofacial
radiology 1996)


Digital subtraction radiography for
assessing alveolar bone
grafts:diagnostic accuracy and
sensitivity
• Maruko and Forbes ( 1993 )


Ultrasonography


• By definition ultra sound has a
periodicity of greater than 20 kHz
• It is distinguished from other wave
forms simply having a vibratory
frequency greater than the audible
range.
• Diagnostic ultrasonography, the clinical
application of ultrasound uses wave on
the frequencies of 1 to 20 MHz

How they work
• Scanners used for sonography
generate electrical impulses that are
converted to high frequency sound
waves by a transducer.
• The transducer consists of a thin piezo
electric crystal or material made up of
great number of dipoles arranged in a
geometric pattern.

• Most commonly used piezoelectric
crystal is lead zirconate.
• The electrical impulse generated by
scanner causes dipoles within the
crystal to realign themselves in the
electric field .
• This causes a change in the thickness
which releases a series of vibrations
that produces sound waves.

• An ultra sound beam passes through or
interacts with the tissues of different acoustic
impedance,it is accentuated by a combination
of absorption, reflection, refraction and
diffusion.
• Sonic waves that are reflected back to the
transducer cause a change in thickness of
piezoelectric crystal, which in turn produces a
signal which is processed and displayed on a
monitor.

• Slice thickness of 0.5 mm or less.
• Real time imaging.
• Here image is produced by reflected
portion of the beam


• The fraction of beam that is reflected
back depends on the acoustic
impedance of the tissue and is
characteristic for different tissues.
(internal echo pattern).


Applications
• Imaging of the –
lymph nodes


Applications
thyroid gland


Applications
salivary glands


Applications
Post surgical oedema and haematoma
Thickness of the masticatory mucosa
Displacement of soft tissue under forces of
occlusion


Comparative data on facial
morphology and muscle thickness
using ultrasonography

• Fiikreet et al( EJO 2005)


Xeroradiography


• New method for recording images
without film.
• based on an electrostatic process
(similar to those used in paper copiers)


Types of systems
• Medical 125 system (since 1970s)
• Dental 110 system (recently developed)


How they work
• Image is recorded on a selenium
coated plate.
• Selenium plate given an electrostatic
charge in a conditioner.
• Then the plate is exposed and the
x-rays penetrate the body parts and
strike the plate causing an electrical
discharge.

• The amount it discharges equals to the
amount of radiation striking the
receptor.
• The patter of electrical charge is
referred to as a latent image.
• This is converted to visible image by a
process called development.


Figure of process


Development
• The plate is exposed to a cloud of
charged powder particles called as
toner.
• Individual toner particles are attracted
to surface of the plate .
• The association of the toner and plate is
related to the distribution of the charge
and is controlled by electric fields.

Dental 110 system
• Similar to the medical 125 system in
concept is physically different.
• The plates are of 1 and 2 size and fit
conveniently into the oral cavity.
• The plates are charge and developed in
a single piece of equipment.


Advantages
• Edge enhancement (deposition of more toner
to the high charge side of the boundary and
less toner on the low charge side )
• A choice of positive and negative displays
• Good detail
• Wide exposure of latitude. (imaging of objects
of broad range of densities in a single
exposure)


Applications
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Mammography
Cephalometrty
Sialography
Detection of caries and alveolar bone
height ( progress of periodontal
diseases).
• Detection of oral cancer
• Imaging of bio materials.

TMJ tomography
• Bony margins are see in more detail
and sharply.
• Halender et al and Castrup and Shwatz
showed no significant difference
between tomographic images and
xeroradiographs.


The role of xeroradiography in
cephalometry
• Davis et al (Journal dent 1977)


Radiologic exposure conditions And
resultant skin doses in application of
xeroradiography to orthodontic
diagnosis

• Nakasima et al (AJO DO 1980)


Conventional radiography vs.
xeroradiography
• Edge enhancement and wide latitude
• Greater ability to resolve structures
• Greater visualization of minute details of
bone and teeth.
• Require about one third exposure of
conventional film.


Laser holography


Laser
• Light amplification by stimulated
emission of radiation.
• Coherence is the key property. (means
all the waves of light are going up and
down together )


Holography
• Holos means whole
• Gramma means message
• An advanced form of photography,
allows an image to be recorded in
dimensions.


3

History
• Denis Gabor – 1947 (Hungarian
physicist).
• Not until laser holography was so
popular. (conventional light sources
gave too little light or too much light).


Lasers how they work
• Depends of certain characteristics of
certain atoms which have been raised
to an excited state,which when brought
back to ground state release a package
of electromagnetic radiation .


Two types of lasers
• Helium neon laser


Two types of lasers
• Pulse ruby laser


Holography basics
• Two step lens less imaging process
called as wavefront construction.
• An interference between the object field
and background wave (reference wave)
is formed and recorded with
photographic material.
• The aim is to record both amplitude and
phase.


• The record known as hologram
captures the complete wave which can
be viewed at later date with appropriate
illumination.
• The object can be considered to be
made up of a number of point sources
distributed in 3 dimensions.


• Because of need for interference
between the reference and object
beams, holograms typically need a
laser to produce them
• The light from laser produces two
beams one is the reference beam and
the other illuminating the object called
as object beam

Types of holograms
• Reflection hologram
- most common type seen in
galleries
• Transmission hologram
- visa card


Holography in medicine


X ray holography
• Imaging of internal body parts of the
body and living biological specimens
with very high resolution without the
need for sample preparation.


Multiplexed holography
• Complete display of 3d tomographic
medical data.
• Used in prostheses and craniofacial
surgery .
• Volumetric multiplexed holograms.


Endoscopic holography
• Potential for providing a powerful tool
for non contact high resolution 3d
imaging and non destructive
measurements inside natural cavities of
human body or in any difficult to access
environment.


Orthodontic applications
• Holographic study of variations in bone
deformations resulting from different
head gear forces in a macerated human
skull (Andrej Zetner – AO 1995 )


Holographic determination of the
centre of rotation produced by
orthodontic forces
• Burstone et al (AJO – DO 1980)


Specialized radiographic techniques

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Specialized radiographic techniques /certified fixed orthodontic courses by Indian dental academy

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